[Pw_forum] How to read lattice constant from the output file of vc-relax

[姚新欣]

Dear all,

I execute a vc-relax calculation, the output file is like this:

===============================================================================

!    total energy              = -1513.15280271 ryd
     estimated scf accuracy    <     0.00000005 ryd

     total magnetization       =     9.00 Bohr mag/cell
     absolute magnetization    =     9.12 Bohr mag/cell

     convergence has been achieved

     Forces acting on atoms (Ry/au):

     atom   1 type  1   force =    -0.00090234   -0.00090236   -0.00060040
     atom   2 type  3   force =     0.00025524    0.00025523    0.00032448
     atom   3 type  4   force =    -0.00023451   -0.00017762    0.00005756
     atom   4 type  4   force =    -0.00017761   -0.00023452    0.00005754
     atom   5 type  4   force =    -0.00014720   -0.00014719   -0.00004334
     atom   6 type  5   force =     0.00021078    0.00021077    0.00024824
     atom   7 type  2   force =     0.00072939    0.00072938   -0.00007323
     atom   8 type  3   force =     0.00030165    0.00030164    0.00012308
     atom   9 type  4   force =     0.00015559    0.00030045   -0.00009079
     atom  10 type  4   force =     0.00030045    0.00015558   -0.00009079
     atom  11 type  4   force =     0.00009477    0.00009474    0.00003522
     atom  12 type  4   force =     0.00037284    0.00037287    0.00023032
     atom  13 type  3   force =    -0.00010083   -0.00010056   -0.00011395
     atom  14 type  3   force =    -0.00014817   -0.00014817   -0.00041716
     atom  15 type  4   force =    -0.00008397    0.00000251    0.00014874
     atom  16 type  4   force =     0.00000267   -0.00008405    0.00014871
     atom  17 type  4   force =    -0.00011380   -0.00011380   -0.00003731
     atom  18 type  4   force =    -0.00051496   -0.00051490    0.00009309

     Total force =     0.002310     Total SCF correction =     0.000828


     entering subroutine stress ...

          total   stress  (ryd/bohr**3)                  (kbar)     P=   -0.02
  -0.00000170  -0.00000001   0.00000121         -0.25      0.00      0.18
  -0.00000001  -0.00000170   0.00000121          0.00     -0.25      0.18
   0.00000121   0.00000121   0.00000295          0.18      0.18      0.43


     Parrinello-Rahman Damped Dynamics: convergence achieved, Efinal=
-1513.15280271

------------------------------------------------------------------------

     Final estimate of lattice vectors (input alat units)
   0.999218793   0.004883129   0.003921399
   0.004883129   0.999218813   0.003921395
   0.007955423   0.007955414   2.046656291
  final unit-cell volume =   1413.6989 (a.u.)^3
  input alat =       8.8445 (a.u.)

CELL_PARAMETERS (alat)
   0.999218793   0.004883129   0.003921399
   0.004883129   0.999218813   0.003921395
   0.007955423   0.007955414   2.046656291

ATOMIC_POSITIONS (alat)
Fe1     -0.013056076  -0.013055086   0.002515773
Sn       0.497703713   0.497704623   0.354603733
O        0.719819040   0.305839769   0.021489138
O        0.305838560   0.719819831   0.021489205
O        0.842148687   0.842149758   0.340853449
H        0.219947019   0.219947779   0.341994037
Fe2     -0.013973823  -0.013972857   0.708191013
Sn       0.502042637   0.502043667   1.027340878
O        0.721364873   0.314430703   0.685223918
O        0.314429607   0.721365697   0.685223880
O        0.193695096   0.193695837   1.021346052
O        0.811306594   0.811307850   1.038377647
Sn       0.006642077   0.006643077   1.377214153
Sn       0.505715303   0.505716371   1.729800072
O        0.691583090   0.308332725   1.381201005
O        0.308331230   0.691583732   1.381201013
O        0.192814143   0.192814844   1.745050428
O        0.814855563   0.814856839   1.731663985



     Writing output data file        sno2.save
===============================================================================


I propose to execute another calculation of different replaced positions with
optimized atomic_positions as the initial condition,which I expect to spend less
time to finish,but I am puzzled by the optimized cell_parameters.From previous
outcomes,how can I determine the new cell_parameters and new atomic_positions in
the inputfile?


I have attempted to use a11(the first diagonal element of
cell_parameters)*celldm(1) as the new celldm(1),a33(the third diagonal element of
cell_parameters) as the new celldm(3),the output atomic_positions(alat) as the new
atomic_positions,and neglect all of the nondiagonal elements.
After the first self-consistent,I gain stresses with very large nondiagonal
elements than diagonal elements like that:
===============================================================================
          total   stress  (ryd/bohr**3)                  (kbar)     P=    3.20
   0.00000417   0.00011011   0.00005447          0.61     16.20      8.01
   0.00011011   0.00000418   0.00005447         16.20      0.61      8.01
   0.00005447   0.00005447   0.00005700          8.01      8.01      8.39
===============================================================================
How can I adapt the input parameters to avoid this condition and get smaller
nondiagonal elements?


In the system block of the input file,there is a parameter "nosym".How does it
affect the final results? In my system(1*1*3 units supercells of SnO2
rutile-structure which include 18 atoms,and two Sn atoms are replaced by Fe and
one O atom by H),which value should I select,"true" or "false"?


Any help would be appreciated.

Best regards!


=======================================
X.X.Yao
School of Physics and Microelectronics,
Shandong University,
Jinan,Shandong 250100,
People's Republic of China. 
=======================================